1. Field of the Invention
The present invention relates to a laser dicing sheet suitably used for fixing a work so as to make into chips by dicing with laser beam and a manufacturing method for chip body with suitably using the laser dicing sheet.
2. Description of the Related Art
In recent years, since there is a case that a work is difficult to cut by a blade dicing, a laser dicing is particularly attracted which is capable of cutting the work by the laser dicing. As shown in Japanese Patent Application Laying Open No. 2002-343747, an example of a laser dicing sheet used for the laser dicing is disclosed by the applicant.
In the laser dicing, a work fixed on a dicing sheet is cut by scanning the laser beam. In this case, a focal point of the laser beam moves as following, namely, the focal point is accelerated from a surface of the dicing sheet wherein the work is not attached (an outer edge portion of the work), scanning on a surface of the work at constant speed, the focal point is decelerated at the opposite outer edge portion of the work, then the focal point stops. After that, a movement direction is turned and the focal point of the laser beam is accelerated, scanning on the work surface, the laser beam is again decelerated and stops and turned.
Therefore, at the time of accelerating and decelerating speeds when moving the laser beam focal point, the laser beam is directly irradiated on end portions of the dicing sheet wherein the work is not attached. There is a problem that, at this time, the laser beam transmits through the dicing sheet and a chuck table is damaged. Further, there is a problem that a surface of the dicing sheet, which contacts with the chuck table heated by the laser beam, is melting and is fused with the chuck table.
In order to eliminate these problems, a distance between the work and a surface of the chuck table is lengthened by using a dicing sheet having large thickness which is shown in Japanese Patent Application Laying Open No. 2006-245487. By using this method, the laser beam reached to the chuck table is not focused, therefore, the chuck table is not damaged since an energetic density is low. Further the above mentioned welding problem is not occurred. However, there are sometimes difficult to expand after the dicing because the thickness of a base material is thick.
Also, Japanese Patent Application Laying Open No. 2002-141306 discloses a dicing sheet comprising an adhesive layer on a base material (herein after sometimes called as “polyurethane acrylate film”) obtained from film forming and curing curable resin such as urethane acrylate oligomer and the like. However, in this patent literature, it is intended to apply the blade dicing and specific problems of the laser dicing as mentioned above are not recognized.
It is expected that film damage is relatively minor even though the laser beams is directly irradiated, because a crosslink density of the polyurethane acrylate film is high. Also, because an expanding ability is favorable, it is easy to expand the laser dicing sheet after the dicing to thereby spread the space between chips. Therefore, it should be studied to use polyurethane acrylate film as a base material stated above.
However, in case of using polyurethane acrylate film as a base material of the dicing sheet, there is following concern.
Normally, after expanding process and picking up chips, the dicing sheet adhered on a ring frame is stowed in a recovery cassette and recovered. After recovering, removing dicing sheet from the ring frame, the ring frame is reused via cleaning process and the like. Since the dicing sheet is elongated by expanding, the dicing sheet is sagging from the ring frame. In this status, the sagging dicing sheet cannot be recovered to the recovery cassette smoothly, because the dicing sheet contacts other recovered ring frame and sheet.
For example, although polyurethane acrylate film excelled in expanding ability, it is less shape-restoring.
Therefore, although polyurethane acrylate film is expected to have excellent character as a base material of the laser dicing sheet, there is an impediment in practical use because of poor shape-restoring capability.